1. Field of the Invention
This invention relates a method of producing a reinforcing fiber sheet which comprises reinforcing fibers formed on a supporting sheet through a binder resin layer.
2. Prior Art
Up to this time, a reinforcing fiber sheet has been used in a number of applications in the field of engineering works. In other industrial fields such as machinery and consumer electronics also, the reinforcing fiber sheet is increasingly being used with the aim of improving rigidity and strength.
This reinforcing fiber sheet, as shown in FIG. 14, comprises reinforcing fibers 104 unidirectionally arranged on a releasing paper 102 as a supporting body through a binder resin layer (adhesive layer) 103.
The unidirectional reinforcing fiber sheet 101 is, after impregnating the reinforcing fibers 104 with a matrix resin, wound around an overpass bridge column, and then the resin is hardened to render the reinforcing fiber sheet 101 in to fiber-reinforced plastic, whereby the bridge column can be strengthened and damaged areas repaired.
Conventionaly, the unidirectional reinforcing fiber sheet mentioned above has been produced as shown in FIG. 15. Reinforcing fibers 104 in the form of fiber bundles are supplied to a pair of superposition rollers 132 and to this, releasing papers 102 and 135 are supplied from above and below, and then the reinforcing fibers 104 are sandwiched between releasing papers 102 and 135 by the superposition rollers 132. At this time, a binder resin layer 103 is formed on one releasing paper 102 by application roller 150. Next, the superposed layers are sent to a heating and pressurizing section 140, consisting of a pair of pressure rollers 138 and heaters 139 disposed before and after the rolleres; the superposed layers are then heated and pressed. As a result, the fiber bundles of reinforcing fiber 104 are slightly taken apart and the reinforcing fibers 104 are attached on the releasing paper 102 with the aid of binder resin layer 103. After that, the other releasing paper 135 is peeled off at the location of a pair of guide rollers 141, and a reinforcing fiber sheet 101 is obtained. The reinforcing fiber sheet 101 thus obtained is wound by a winding roller 146.
However, the coating of the binder resin layer 103 on the releasing paper 102 is carried out by adhering a resin made into a thin film 102 by the application roller 150 onto the releasing paper and for this reason, adjusting the thickness of the resin film is time consuming. Also, since the entire coating device increases in size, realistically, the coating device cannot be placed in the reinforcing fiber sheet production line and consequently, 2-stage production becomes necessary, wherein a binder resin layer is coated on the releasing paper outside the production line, this resin coated releasing paper is wound once, then placed back into the production line. For this reason, the coating of a binder resin layer 103 has heretofore been a very time-consuming procedure and the production efficiency of reinforcing fiber sheet has been low.
Thereupon, the present inventors carried out intensive research into a coating method in which a resin liquid is coated onto the reinforcing fiber so as to form the binder resin layer on the reinforcing fiber with less time and trouble by using a spray device. As a result, the present inventors found out that when a special spray device having a plurality of nozzles tipped with capillary tubes positioned in gas discharge pores is used and a molten resin liquid is blown out onto the reinforcing fibers from the ends of the capillary tubes by heated streams of air blown out from the gas discharge pores, the molten resin liquid becomes droplets of an appropriate size to thereby adhere to the reinforcing fibers, so that a thin binder resin layer can be formed onto the reinforcing fibers and also the time and effort required for the coating is reduced.